1. Field of the Invention
The present invention relates to a bearing cooling system in which a heat pipe is formed in a rotary shaft of a horizontal shaft water turbine generator.
2. Description of the Prior Art
Generally, in a bearing cooling system in a horizontal shaft water turbine generator having an output of not less than approximately 1,000 kw, lubricating oil is cooled by a water cooling type oil cooler and circulated by a water circulating pump. FIG. 26 shows a bearing cooling system using a water cooling type oil cooler in a conventional horizontal shaft water turbine generator provided with a journal bearing 1 and a thrust bearing 3. The heat generated from the journal bearing 1 and the thrust bearing 3 is absorbed by lubricating oil 5. The lubricating oil, which has absorbed the heat, is cooled by a separately provided water cooling type oil cooler 10 having a water supply pump 13 and a water supply piping 14 and is circulated to the journal bearing 1 and the thrust bearing 3.
However, the bearing cooling system using a water cooling type oil cooler for cooling the lubricating oil 5 has a disadvantage in that it requires expensive equipment such as a water feeding pump 11 and oil piping 12 which require labor for maintenance and inspection. Further, if dirty cooling water is used, the water supply piping 14 may clog or corrode which would cause a failure or water leakage.
FIG. 27 shows a bearing cooling system using a rotary shaft heat pipe of a conventional horizontal shaft water turbine generator. The bearing cooling system includes a bearing stand 2, a rotary shaft 4, a runner (sometimes referred to herein as a moving blade) 6, a rotary shaft heat pipe 7, a vapor space 8, a hydraulic working fluid 20, and a thrust collar 22. In FIG. 27, the inside of the rotary shaft 4 is hollow; and the hydraulic working fluid 20 is sealed in the hollow portion forming a heat pipe with the bearing side of the rotary shaft 4 as a heat generating portion and with the vapor space 8 of the moving blade 6 as a condensing portion.
In FIG. 27, most of the heat generated at the journal bearing 1 and at the thrust bearing 3 flows into the rotary shaft heat pipe 7. During that time the heat resistance increases in the thrust bearing 3 side from the heat generating portion of the thrust collar 22 to the heat pipe surface, i.e., the temperature difference therebetween is large, and the heat resistance on the evaporating surface of the heat pipe increases. The difference in temperature is great due to the fact that the heat flux becomes large for the following reasons:
(1) There is a long distance between the heat generating portion and the evaporating surface of the heat pipe for heat conduction.
(2) The heat conductivity in the thrust collar 22 and the heat flux (W/cm.sup.2) on the evaporation surface of the heat pipe are both large.
(3) Generally, the thrust collar is designed so as to be uniform in thickness. Thus, the heat conduction area as well as the area of the evaporating surface decreases from the heating portion of the thrust collar 22 toward the central portion of the rotary shaft. Accordingly, the temperature at the bearing portion may exceed an allowable limit, so that it was difficult to cool the thrust collar with the bearing cooling system of the horizontal shaft water turbine generator which has an output of not less than approximately 1,000 kw.
FIG. 28 shows a bearing cooling system using another rotary shaft heat pipe, in which a hollow portion 26 is provided in a thrust collar 22 so as to communicate with a condensing portion of a rotary shaft heat pipe 7. In this bearing cooling system, however, at a heat conduction portion between the heat generating portion of the thrust collar 22 of the thrust bearing 3 and the hydraulic working fluid (onto which large thrust force is applied), at a heat conduction portion between the heat generating portion of the journal bearing 1 and the hydraulic working fluid 20, and at a heat conduction portion between the hydraulic working fluid 20 on the side of a water turbine and flowing water, the more the output is increased, the more the thrust force and the bearing load increase, so that the shaft is increased in thickness as well as in size so that the heat loss increases and heat flux also increases. Accordingly, the heat conduction resistance (a temperature difference) becomes large at each heat conduction portion because the heat resistance is in direct proportion to the product of the heat conduction distance and the heat flux, so that, also in this case, the temperature at the bearing portion may exceed an allowable limit and it is difficult to cool the thrust collar to the bearing cooling system of the horizontal shaft water turbine generator which has an output of not less than approximately 1,000 kw.
Conventionally, in a valve turbine and a Kaplan turbine, a hole is formed in a rotary shaft thereof which causes a water turbine runner vane angle to be variable in accordance with the output of the turbine. Accordingly, it is difficult to use a shaft hole of the rotary shaft of such a turbine as a rotary shaft heat pipe.